Multiwavelength light sources are highly useful for testing WDM optical communication systems and components and as light sources for such systems. A multiwavelength light source is a light source which emits light in a plurality of spectrally spaced apart wavelength channels. In WDM optical communications system, an optical fiber simultaneously carries many different communications channels in light of respectively different wavelengths. Typically 8, 16 or 32 different wavelength signals propagate through the system. In testing WDM systems, components and test equipment, test sources are needed which produce light in the specific channels of the systems.
Typical multiwavelength sources utilize separate sources, such as ECL lasers, for each channel. The separate channels are generated one at a time and then combined to generate a multiwavelength source. This approach is expensive and inefficient.
Researchers have tried to generate multiwavelength sources by creating several very short lasers in a single piece of erbium doped fiber (EDF). This approach has proved inefficient and produces unstable lasers.
Others have used polarization inhomogeniety or spectral inhomogeniety in combination with wavelength selective elements to make an EDF laser with multiple laser wavelengths. But no truly stable, easily manufactured source has been found.
In yet other attempts, broadband light has been generated in EDF by amplified spontaneous emission (ASE) and, by means of filters, divided into several spectral bands. However, such sources produce poor power output in each channel because much of the power generated in the ASE source is between channels and is lost. Accordingly there is a need for an efficient, inexpensive multiwavelength light source.